1. The Field of the Invention
The present invention relates to specialized catheters used in the treatment of thromboembolic occlusions in a patient's circulatory system. More specifically, the present invention relates to improved catheters which deliver thrombolytic fluids to the site of a thrombus or blood clot and which provides an improved lateral dispersion, or spray pattern, of the thrombolytic fluid.
2. The Relevant Technology
A reasonably common and dangerous medical condition arises when a blood clot develops in a patient's circulatory system. A blood clot or thrombus can endanger the health of a patient in at least two significant ways. First, the clot may restrict or even completely stop essential blood flow to a portion of the patient's body. If the blood flow to the brain or heart for example is restricted the patient's life may be placed in jeopardy. Additionally, a clot may break loose from the site at which it formed and be carried by the blood stream to an organ, such as the heart, where it may cause irreparable damage or even death. Accordingly, when a blood clot is detected, it must be quickly and effectively treated.
One method involves surgery to remove the clot and repair the blood vessel, another method mechanically breaks up an existing clot into smaller micro-emboli. A less invasive method uses thrombolytic drugs to break up, or lyse, the thrombus. This method of treating a blood clot consists of inserting a catheter into the patient's circulatory system, preferably near the site of the clot. If the catheter enters the circulatory system near the clot, the catheter alone may be used. If, for a variety of reasons, the catheter must be inserted into the circulatory system at a distance from the clot, placement of the catheter may be aided by using a guide wire or introducer sheath, which can be used to push and guide the catheter through the vessels or arteries of the circulatory system to reach the clot.
Once the catheter is positioned at the site of the clot, a thrombolytic fluid capable of dissolving the clot, such as urokinase or streptokinase, is delivered to the site of the clot by means of the catheter. Conventional catheters have a lumen, i.e., an internal passage, that allows the thrombolytic fluid to flow through the catheter to one or more discharge openings, or sideholes, at or near the distal end of the catheter. The discharged thrombolytic fluid then dissolves or lyses the clot, thus removing the danger to the patient.
Not all clots are easily or successfully lysed. Some clots form around arterial lesions, which clots may not be easily lysed or broken up by the thrombolytic fluid and which usually require surgical removal. Additionally, some clots may be extremely thick, extending for a relatively long distance through a blood vessel of the circulatory system. Such a thick clot may require considerable amounts of time and heavy irrigation of thrombolytic fluid to dissolve.
Typically, a guidewire is used in conjunction with a catheter to facilitate placement of the catheter. The guidewire can also serve to penetrate the clot in order to form a passage therethrough so that the catheter can be inserted within the interior of the clot. This helps to ensure that the thrombolytic fluid is concentrated or focused at the location of the clot, since excessive thrombolytic fluid in the bloodstream can have adverse effects on the patient.
After the guide wire has been used to create a narrow passage through the clot, particularly a thick clot, the thrombolytic fluid is released through the one or more openings within the catheter. In the beginning stages of thrombolytic therapy, thrombolysis was carried out using a catheter with a single opening at the distal end of the catheter. McNamara, T., "Role of Thrombolysis in Peripheral Arterial Occlusion," Am. J. Med., Vol. 83 (Suppl. 2A), pp. 6-10, Aug. 24, 1987. Methods employing a simple catheter required movement of the catheter from one end of the clot to the other while dispensing the thrombolytic fluid in order to adequately distribute the fluid over the entire length of the thrombus.
Subsequent improvements have been made in an attempt to create a more uniform distribution of thrombolytic fluids along the length of the blood clot. A catheter having slits or other pressure activated one-way openings arranged radially at 90.degree. intervals around the circumference of the catheter and in sets of four longitudinally spaced intervals along the length of the catheter is disclosed in U.S. Pat. No. 5,250,034 to Applying et al. A hollow infusion guidewire having sets of four holes, each hole radially separated by 90.degree. intervals around the circumference of the guidewire and each set of four holes spaced longitudinally along the length of the guidewire is set forth in U.S. Pat. No. 5,569,197 to Helmus et al. Catheters having holes individually spaced at regular intervals along the length of the catheter and spaced radially at 90.degree. intervals relative to each previous hole are set forth in U.S. Pat. Nos. 4,968,307 and 4,927,418 to Dake et al.
Whether the infusion holes are grouped together in sets of four holes spaced at 90.degree. intervals around the catheter or staggered to form a spiral configuration with individually staggered holes spaced at 90.degree. intervals, the result is the same: infusion holes that are arranged along four parallel lines radially spaced at 90.degree. intervals around the catheter wall. Although such hole patterns are superior to a simple catheter having a single hole at the distal end, they are only able to distribute thrombolytic fluids at discrete 90.degree. intervals around the circumference of the catheter. The area between the 90.degree. intervals does not receive as much thrombolytic fluid, thus resulting in a poor overall distribution of thrombolytic fluid.
Another difficulty within the art is the uneven longitudinal flow distribution associated with typical infusion catheters. In such typical catheters, fluid discharge pressure decreases as the fluid flows longitudinally along the length of the catheter. Fluid discharge is typically greatest at the holes closest to the fluid source and is least at the holes farthest from the fluid source. The lowering in downstream pressure results from the friction encountered as the fluid flows within the infusion length and from the flow of fluid out of preceding holes. Thus, as fluid escapes from the upstream holes, the downstream fluid pressure is lowered.
As a result, the upstream portion of a blood clot receives more thrombolytic fluid than the downstream portion of the clot. This non-uniform longitudinal flow distribution can require movement of the catheter from one end of the clot to the other end while dispensing fluid in order to adequately distribute the fluid.
Accordingly, there exists a need in the art for improved catheters which can more completely and evenly disperse thrombolytic fluid around the circumference of a catheter in order to more effectively and efficiently lyse blood clots in a patient's blood vessel. There also exists a need for improved catheters which ensure a more consistent dispersion rate between catheters of different infusion lengths. There also exists a need for improved catheters having a more uniform flow distribution along the infusion length of a catheter.